This invention concerns the selective preparation of ethanol from synthesis gas. More particularly, the invention concerns reaction of carbon monoxide and hydrogen in the presence of a product-specific catalyst to produce ethanol.
The preparation of hydrocarbons and oxygenated hydrocarbons from synthesis gas (essentially a mixture of carbon monoxide with varying amounts of carbon dioxide, and hydrogen), has received extensive study and has achieved commercial adoption. Reaction conditions generally involve temperatures on the order of 150.degree.-450.degree. C., pressures of from atmospheric to about 10,000 psig, and hydrogen-to-carbon monoxide ratios in the range of 4:1 to about 1:4 with an iron group, mixtures of metal oxides, or a noble metal group hydrogenation catalyst.
One serious disability of most synthesis gas processes has been the non-selective or non-specific nature of the product distribution. Catalysts which possess acceptable activity generally tend to give a wide spectrum of products--hydrocarbons and oxygenated hydrocarbons--having a broad distribution of carbon atom contents. This not only complicates the recovery of desired products, but results in the wastage of reactants to commercially uninteresting byproducts.
In copending application Ser. No. 541,661 and in its parent Ser. No. 437,141, there has been described a process for the selective preparation of two-carbon atom oxygenated hydrocarbons, namely acetic acid, ethanol, and acetaldehyde, using a rhodium catalyst. It has now been discovered that it is possible to double selectivity toward ethanol, significantly reduce the formation of acetaldehyde and acetic acid, and retain the selectivity toward two-carbon atom oxygenated compounds.